The present disclosure relates to a vehicle control device, and more particularly to a vehicle control device that achieves a desired vehicle attitude (vehicle behavior) by performing an engine control.
Conventionally, devices which control the behavior of a vehicle to a safe direction when the behavior of the vehicle becomes unstable due to a slip, etc. (such as an antiskid brake system (ABS)) are known. For example, devices which detect that a behavior such as understeering or oversteering occurs with the vehicle during cornering, etc. of the vehicle, and apply a suitable deceleration to the wheels so that the behavior is controlled are known.
Meanwhile, a vehicle movement controller is known, that adjusts a deceleration during cornering to control loads applied to front wheels which are steerable wheels so that a series of operations by a vehicle driver (breaking, steering-in, accelerating, steering-back, etc.) during cornering of a vehicle in a normal traveling state become natural and stable, unlike the above control executed for a safety improvement in the traveling state where the behavior of the vehicle becomes unstable.
Further, JP2014-166014A discloses a behavior control device for a vehicle which reduces a driving force (torque) of the vehicle according to a yaw-rate related amount corresponding to a steering operation by a vehicle driver (e.g., yaw acceleration) to quickly decelerate the vehicle when the driver starts the steering operation so that a sufficient load is quickly applied to front wheels which are steerable wheels. According to this behavior control device, a frictional force between the front wheels and a road surface increases and a cornering force of the front wheels increases by quickly applying the loads to the front wheels when the steering operation is started. Therefore, turnability of the vehicle in an early stage of curve entry improves, and a response to the steering-in operation (steering stability) improves. Thus, a vehicle behavior intended by the driver is achieved.
In the behavior control device described in JP2014-166014A, a vehicle attitude is controlled by decelerating the vehicle according to the steering operation by the driver. This vehicle attitude control may be executed by, for example, retarding an ignition timing of an ignition plug of an engine more than in a normal operation (that is, when the vehicle attitude control is not executed), so that an engine torque is reduced. This method is effective especially in a turbocharged engine.
In the turbocharged engine, when reducing the engine torque, the turbocharger is generally controlled to lower a turbocharging pressure. However, if the turbocharging pressure is lowered to temporarily reduce the engine torque in the vehicle attitude control, when increasing the engine torque after the vehicle attitude control, the speed of the turbocharging pressure increase cannot catch up with the torque increase and the acceleration response delays. For this reason, in the turbocharged engine, it is desirable to retard the ignition timing of the ignition plug than in the normal operation so as to reduce the engine torque in a state where the turbocharging pressure is kept substantially constant during the vehicle attitude control.
Meanwhile, when the ignition timing of the ignition plug is retarded, an exhaust gas temperature tends to rise. Therefore, in the above configuration of retarding the ignition timing during the vehicle attitude control, when the vehicle attitude control is frequently executed (e.g., when the vehicle attitude control tends to be frequently executed while the vehicle is traveling on a road, such as, a winding road), the frequency of retarding the ignition timing increases and the exhaust gas temperature becomes high. Particularly, within an operating range where an engine load and/or an engine speed are/is high (e.g., within a turbocharging range of the turbocharged engine), the exhaust gas temperature easily becomes high. When the exhaust gas temperature becomes high, there is a possibility that reliability of engine components (especially, exhaust system components) lowers.